As an interesting example of the opposite UI experience, this video goes into why the McMaster-Carr website is so incredibly snappy to use: https://youtu.be/-Ln-8QM8KhQ.

It's different from GitHub in many ways (no user-generated content, day-by-day mostly static pages), but it's interesting to see how good a browsing experience can be. It makes sense given that their value as a company depends so much on making it quick and easy to find exactly what you need.